The present invention relates in general to an apparatus and method for processing workpieces which minimizes the use of coating materials, and more particularly, to an apparatus and method for applying a layer of a fluid material such as photoresist on the surface of a semiconductor wafer in a manner to reduce the consumption of photoresist being used, while at the same time maintaining or improving uniformity of the coating during processing of the wafer in the fabrication of integrated circuits and the like.
In the processing of workpieces such as semiconductor wafers for the ultimate manufacture of electronic components, one of the steps required is the dispensing of a fixed amount of a certain type of fluid material onto the surface of the wafer. For example, in the manufacture of integrated circuits, a photoresist may be dispensed onto a silicon wafer preliminary to the photoetching of the wafer. In this regard, there is known from U.S. Pat. No. 4,190,015 an apparatus which dispenses a fixed amount of a fluid material onto a semiconductor wafer surface and is then spread evenly thereon, for example, by spinning the wafer at a high rate of speed. The fluid material is discharged from a nozzle in the form of a circular opening formed at the
end of a length of hollow tubing.
U.S. Pat. No. 4,551,355 discloses rotating a disc at high speed on a spindle while fluid carrying magnetic medium material is applied to the disc through a circular dispensing nozzle which starts at the outside of the disc and travels to the inside diameter, pauses momentarily, and then travels back to the outside diameter. As the fluid is applied, a thin film of medium material adheres to the disc while the excess fluid forms a protective coating over this thin film as it flows radially off the disc due to the centrifugal force generated by the high speed rotation. The nozzle discharge pressure and the high rotational speed of the disc results in a very thin film of magnetic medium material being applied to the disc. The rate of nozzle travel can be adjusted to vary the medium material film thickness.
U.S. Pat. No. 3,198,657 discloses a process for spin coating objects with a pigmented material. The surface to be spin coated is first wetted by discharging the material from a cylindrical nozzle onto the spinning surface from the outer edge to the inner edge of the surface to be coated. The discharge of the coating material onto the spinning surface is continued using conventional spin coating techniques. The discharge of the coating material may be continued at the inner edge until an amount of material in excess of the amount necessary to cover the surface has been dispensed. In the alternative, the coating material may be continued at the inner edge only until a wave front of material is flowing outward over the spinning surface. In this event, the material is discharged from the inner edge to the outer edge either by dispensing behind the moving wave front or by pouring over and in front of the wave front. At the outer edge of the surface, discharge of the material is discontinued.
U.S. Pat. No. 4,457,259 discloses a spray apparatus which provides a predetermined, uniform quantity of liquid such as photoresist developer per unit area of surface by a parabolic cam mechanism, arranged to repeatedly reciprocate a circular nozzle at a predetermined linear velocity a plurality of times over a spinning semiconductor wafer. The mechanism moves the nozzle at a parabolic varying velocity such that the liquid is deposited at a uniform quantity per unit area. The cam is continuously rotated and engaged with a cam follower by a programmable timer which defines the spray period. A similar apparatus which dispenses the fluid through a circular nozzle in the form of a continuous spiral bead on a semiconductor wafer by means of a cam and cam follower arrangement is known from U.S. Pat. No. 4,451,507.
U.S. Pat. No. 4,267,212 discloses a process for spin coating a semiconductor wafer uniformly with a coating solution such as a photographic emulsion by rotating the wafer at a first speed while simultaneously applying the coating solution through a circular nozzle at a radially moving position. Once the semiconductor wafer has been initially covered, the speed of rotation of the wafer is increased and rotation continues until a uniform coating has been obtained. A similar process having a stationary nozzle is disclosed in U.S. Pat. No. 3,695,928.
In each of the aforedescribed apparatuses and methods, the fluid coating material is dispensed in a column of fluid whose cross-section approximates a circle, either during wafer rotation or while the wafer is stationary. Wafer coating is achieved by building up a pool of the fluid coating material in the nature of a thick layer and spin casting a film thereof by accelerating the rotation of the wafer about its own center in order to remove the excess material and to leave a thin film coating therebehind. The amount of fluid coating material, such as photoresist, remaining on the wafer is known to be a very small fraction of the amount that is initially dispensed, approximately one part in one thousand. This results in a substantial material loss of unusable photoresist along with its attendant cost. In addition, this creation of a pool of the fluid coating material on the wafer surface can result in the formation of uneven films which might adversely effect subsequent wafer processing.
Accordingly, there is an unsolved need for an apparatus and method which minimizes consumption of the coating material, such as photoresist, during spin casting and the like, as well as providing a more uniform thin film coating on semiconductor wafers during the fabrication of integrated circuits and other electronic components therefrom in the semiconductor industry.